In the first generation, there weren't any types that were super effective to two starter types. I guess it'd be unfair for Poison to be the exception.I just understand why it is only SE against grass..when it could also be SE against water and Dragons.
By that logic, Psychic should be super effective against Dark, and Dark should be super effective against Fighting, since opposites are supposed to be good against each other.And i never really understood why grass isn't SE against poison!!! Herbal remedies > poison!!